Marco Rubio has a plan for paid parental leave. The fact that this isn’t something you might expect from a conservative Republican running for president makes it a pretty good indicator of how popular the idea has become. According to one survey last year, two-thirds of Americans think employers should have to give new parents paid time off to care for their child, a belief shared by majorities of Democrats, Republicans, and Independents.

One likely reason support for paid parental leave is so popular is because it’s in such noticeably short supply in the United States. As voters have been reminded in more than one stump speech, the U.S. is the only industrialized country that doesn’t have any paid parental leave laws on the books at a national level.

But while only three U.S. states offer some form of paid parental leave to full-time, private-sector workers, the push to do more might finally be gaining steam. Here’s a look at where we are and how far there’s left to go.

Bill Clinton signed the Family Medical Leave Act (FMLA) into law within weeks of taking office in 1993. It was landmark legislation passed with bipartisan support, but there’s a lot it leaves out. The law lets people who've worked at companies of 50 or more employees for at least a year take up to 12 weeks off for childbirth and adoption or foster care placement; to care for an ill parent, child, or spouse; or to deal with a serious health condition of their own, all without having to worry about getting fired. But that guaranteed time off is completely unpaid, and needless to say, many people find it difficult if not impossible to go without any income for three months.

That’s one reason why a handful of states and municipalities have since passed their own paid leave laws, most geared toward new parents. But that’s made for a quite messy patchwork of coverage.

So far only California, New Jersey, and Rhode Island offer statewide paid family leave for private-sector workers, all with different provisions. In 2007, Washington state passed a law that included a paid leave insurance program but legislators left it unfunded, and 14 other states and Washington, D.C. have passed measures that expand upon the FMLA in at least one way, short of offering paid leave.

Some of those expansions are modest, covering only state employees or offering limited accommodations for only pregnant women under state anti-discrimination laws. (Four states have also passed laws widening access to paid sick leave, with Vermont set to become the fifth, but those don’t cover workers’ family members.)

Paid leave programs now also exist in Kansas City, Austin, San Francisco, Boston, and New York City, offering combinations of paid sick leave for individual workers and paid family leave to care for their children, parents, and spouses, generally for up to six weeks every year. Earlier this month Defense Secretary Ashton Carter announced new rules for paid leave for military families, entitling service members across all branches to 12 weeks off. (The Marines and the Navy previously had 18-week programs, which will be shortened under the new provisions.)

New York state is considering a law that experts say would be among the most progressive in the country, mandating up to 12 weeks of paid family leave for workers, with coverage starting at 35% of their salaries in the first year of the law's enactment and climbing to 50% after 2020. The effort is being spearheaded by Governor Andrew Cuomo and got backing last year from Vice President Joe Biden. While the bill before New York’s Senate is the fifth such measure to clear the State Assembly and its fate doesn’t look good, Cuomo has also included a 12-week paid leave plan as part of his 2016 budget proposal, giving the legislature another opportunity to enact it.

Legislation is also up for consideration in Washington, D.C., Maryland, Connecticut (each of which, like New York, has previously expanded on the FMLA), and Delaware, among a slate of efforts in other states that haven’t yet gained as much momentum.

Regardless of which state you live in the patchwork of policy still leaves a lot of workers with no protection at all. For one thing, employees of small businesses are left out of even the most generous protections in states with expanded coverage. The FMLA doesn’t even offer unpaid family leave for workers at companies with fewer than 50 employees, and the smattering of recent paid leave measures have similar firm-size thresholds.

And that’s just one variable that differs substantially state by state. Few paid leave programs guarantee employees 100% of their wages while they aren’t working, and the time periods they’re entitled to vary. Some laws accommodate mothers better than fathers, and California, for instance, offers paid parental leave with no job-protection guarantees. The list goes on.

There’s also the difficulty of estimating just how many people are covered by the measures already on the books. As the Wall Street Journal reports, the Department of Labor found last year that 12% of private-sector workers had access to some form of paid parental leave, while a separate government survey found some 48% of employees reporting access—formal or otherwise—to family-related paid leave as early as 2011. And it goes without saying that many other types of workers (like freelancers) whose incomes don’t come in biweekly paychecks also lie outside the safety net that even the most ambitious of paid leave laws seek to widen.

What’s becoming clearer, though, is that their socioeconomic benefits may outweigh the costs. Some 90% of California employers have said the state’s paid leave law had either positive or no discernible impacts on business, while the use of maternity leave doubled, with the most growth among lower-income workers. And as a result, the weekly wages and working hours of mothers with young children both increased by around 17%. Private company policies (such as those in place at major tech companies) have also been proven to attract and retain talented employees.

For many lawmakers and activists concerned with paid leave, the ultimate goal is national action on par with what the FMLA did for unpaid leave. Increasingly, the squabble is less about whether to act than how. Republicans tend to favor tax credits to incentivize businesses to expand their policies, the model that Rubio’s plan is based on. It's also the approach reflected in one Senate bill vying against another that's supported by Democrats, which would offer 12 weeks of leave at two-thirds of workers wages, paid for by a 0.4% increase in payroll taxes split between employees and employers.

It’s this model that advocacy organizations tend to favor. "Tax credits in our view fall short," Vicki Shabo, Vice President at the National Partnership for Women & Families, tells Fast Company, "because they are entirely dependent on the employer...and there’s no evidence that they change or incentivize employer behaviors . . . [so] you end up perpetuating the inequality that already exists in terms of access to paid leave."

Indeed, voluntary action along those lines has been limited mainly to top tech companies like Amazon, Netflix, Spotify, and Adobe, among others, but employers that aren’t competing for high-demand skilled talent aren't as likely to follow suit unless compelled.

Some think it’s only a matter of time before they are. At a minimum, there’s never been more reason for that optimism than there is right now.

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